This is a complicated sign. It has as much to do with the example you set for your child as anything. Your setting a good example will help as will letting him know you think time is important.
Be sure you can answer Yes to these questions. Are you usually on time? Do things happen at regular times such as dinner time? Do you usually get everything done you planned for the day? When you tell him it will be a few minutes, does it really happen in a few minutes? Be sure you are setting a good example.
Here are a couple more points. Doing school work has a lot to do with time management. He needs to get to school on time and get to class on time after he gets to school. He needs to do school work in the time he is given to do it and then turn it in on time. He needs to figure out how long work will take and pace himself so he gets it done.
Your child's problems usually are because of several things. Not seeing how long things will take is the most common. Getting better at this requires thinking about it, making estimates and seeing how they work out and remembering how long it took the last time.
Another common problem is not keeping at it. Putting off starting, getting distracted, day-dreaming, quitting before finishing and other bad habits get in the way.
This sign may be part of a more general learning problem; but it usually is not. It usually has mostly to do with bad work habits and not staying with it.